Commit 41a5db8d8161 ("Add support for non-fix-size percpu mem allocation")
added support for non-fix-size percpu memory allocation.
Such allocation will allocate percpu memory for all buckets on all
cpus and the memory consumption is in the order to quadratic.
For example, let us say, 4 cpus, unit size 16 bytes, so each
cpu has 16 * 4 = 64 bytes, with 4 cpus, total will be 64 * 4 = 256 bytes.
Then let us say, 8 cpus with the same unit size, each cpu
has 16 * 8 = 128 bytes, with 8 cpus, total will be 128 * 8 = 1024 bytes.
So if the number of cpus doubles, the number of memory consumption
will be 4 times. So for a system with large number of cpus, the
memory consumption goes up quickly with quadratic order.
For example, for 4KB percpu allocation, 128 cpus. The total memory
consumption will 4KB * 128 * 128 = 64MB. Things will become
worse if the number of cpus is bigger (e.g., 512, 1024, etc.)
In Commit 41a5db8d8161, the non-fix-size percpu memory allocation is
done in boot time, so for system with large number of cpus, the initial
percpu memory consumption is very visible. For example, for 128 cpu
system, the total percpu memory allocation will be at least
(16 + 32 + 64 + 96 + 128 + 196 + 256 + 512 + 1024 + 2048 + 4096)
* 128 * 128 = ~138MB.
which is pretty big. It will be even bigger for larger number of cpus.
Note that the current prefill also allocates 4 entries if the unit size
is less than 256. So on top of 138MB memory consumption, this will
add more consumption with
3 * (16 + 32 + 64 + 96 + 128 + 196 + 256) * 128 * 128 = ~38MB.
Next patch will try to reduce this memory consumption.
Later on, Commit 1fda5bb66ad8 ("bpf: Do not allocate percpu memory
at init stage") moved the non-fix-size percpu memory allocation
to bpf verificaiton stage. Once a particular bpf_percpu_obj_new()
is called by bpf program, the memory allocator will try to fill in
the cache with all sizes, causing the same amount of percpu memory
consumption as in the boot stage.
To reduce the initial percpu memory consumption for non-fix-size
percpu memory allocation, instead of filling the cache with all
supported allocation sizes, this patch intends to fill the cache
only for the requested size. As typically users will not use large
percpu data structure, this can save memory significantly.
For example, the allocation size is 64 bytes with 128 cpus.
Then total percpu memory amount will be 64 * 128 * 128 = 1MB,
much less than previous 138MB.
Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
---
include/linux/bpf_mem_alloc.h | 5 +++
kernel/bpf/memalloc.c | 62 +++++++++++++++++++++++++++++++++++
kernel/bpf/verifier.c | 23 +++++--------
3 files changed, 75 insertions(+), 15 deletions(-)
diff --git a/include/linux/bpf_mem_alloc.h b/include/linux/bpf_mem_alloc.h
index bb1223b21308..b049c580e7fb 100644
--- a/include/linux/bpf_mem_alloc.h
+++ b/include/linux/bpf_mem_alloc.h
@@ -21,8 +21,13 @@ struct bpf_mem_alloc {
* 'size = 0' is for bpf_mem_alloc which manages many fixed-size objects.
* Alloc and free are done with bpf_mem_{alloc,free}() and the size of
* the returned object is given by the size argument of bpf_mem_alloc().
+ * If percpu equals true, error will be returned in order to avoid
+ * large memory consumption and the below bpf_mem_alloc_percpu_unit_init()
+ * should be used to do on-demand per-cpu allocation for each size.
*/
int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu);
+/* The percpu allocation is allowed for different unit size. */
+int bpf_mem_alloc_percpu_unit_init(struct bpf_mem_alloc *ma, int size);
void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma);
/* kmalloc/kfree equivalent: */
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 75068167e745..84987e97fd0a 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -526,6 +526,9 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
struct bpf_mem_cache *c, __percpu *pc;
struct obj_cgroup *objcg = NULL;
+ if (percpu && size == 0)
+ return -EINVAL;
+
/* room for llist_node and per-cpu pointer */
if (percpu)
percpu_size = LLIST_NODE_SZ + sizeof(void *);
@@ -625,6 +628,65 @@ static void bpf_mem_alloc_destroy_cache(struct bpf_mem_cache *c)
drain_mem_cache(c);
}
+int bpf_mem_alloc_percpu_unit_init(struct bpf_mem_alloc *ma, int size)
+{
+ static u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096};
